The radiofrequency (RF) spectrum is a finite resource. As the number of operators (i.e., users) and applications have grown, some RF bands, such as the Unlicensed National Information Infrastructure band (i.e., UNII band) or the Industrial, Scientific, and Medical band (i.e., ISM band) have been co-allocated for a variety of applications and users. To prevent interference among the different applications, certain devices are required to monitor co-allocated band channels and to take action when interference is detected. In the United States, for example, wireless local area network (i.e., WLAN) devices (e.g., 802.11 a/h devices) may operate in a 5 GHz band, which was traditionally allocated for use by radar (e.g., weather radar), but must tune to a different channel when interference is detected. This interference avoidance process is referred to a Dynamic Frequency Selection (DFS).
Conventional DFS operations cause a wireless access point device operating in a given channel to switch to another channel when a potential for interference (e.g., the presence of a radar signal) is detected. Typically, a wireless device (e.g., wireless access point) running DFS continuously monitors (i.e., both prior to and during channel use) the channel of use (i.e., the service channel) for the presence of a radar signal. Once detected, the device vacates and/or flags the channel as unavailable. Vacating a channel and relocating to a new channel is disruptive to communication and can result in the device having to broadcast a channel switch announcement, disassociate with existing client devices, search for a new channel, switch to the new channel, and accept to new client associations.
Because radars typically transmit at high powers (e.g., between 250 kilowatts and 1 megawatt), a radar may leak signals (e.g., intermodulation products) into the service channel even when the radar is operating on a different channel. This situation may cause a false DFS detection. This false DFS detection may unnecessarily trigger the wireless device to tune to another operating frequency or channel. In addition, false DFS detection (i.e., DFS falsing) can limit the number of available channels when a device is searching for open channels.
In certain circumstances, it is desired that signals resulting from radars operating on-channel be distinguished from signals resulting from radars operating off-channel to reduce or eliminate unnecessary DFS operations.